With the recent trend for higher performance and more multifunctional electronic devices, batteries with improved volume energy density have been used. However, such high energy-density batteries may undergo thermal runaway in the event of internal shorting due to deformation under external pressure.
In this connection, silica or alumina is often disposed between the battery positive and negative electrodes in a laminar fashion to improve battery safety. In the related art, the following literatures are available.
JP-A-2010-129449 describes a secondary battery that uses lithium bis(fluorosulfonyl)imide (LiFSI) as the electrolyte salt, and a halogenated carbonate ester-containing solvent for dissolving the electrolyte salt.
JP-T-08-511274 describes a secondary battery that uses lithium bis(fluorosulfonyl)imide as the electrolyte salt. JP-A-2004-165151 describes improving stability under high temperature or during the storage with the use of an electrolytic solution that contains lactone as the solvent, and lithium bis(fluorosulfonyl)imide as the electrolyte salt. This publication also describes further improving stability with the use of an electrolytic solution that further contains vinylene carbonate, vinylethylene carbonate, phenylethylene carbonate, or propanesultone as an additive. JP-A-2009-70636 describes a battery that contains a quaternary ammonium cation together with a FSI (fluorosulfonylimide) anion and an inorganic anion. JP-T-2001-519589 describes using a phosphoric acid ester and a boric acid ester together.